The present invention generally relates to a template for measuring a distance from an edge of a disk and a method of using the template and more particularly, relates to a template for measuring a distance from a wafer edge after an edge bead rinse process to determine how well the process is centered with the wafer and a method of using the template.
Spin-on-glass (SOG) is frequently used for gap fill and planarization of inter-level dielectrics (ILD) in multi-level metalization structures. It is a suitable material for use in low-cost fabrication of IC circuits. Most commonly used SOG materials are of two basic types; an inorganic type of silicate based SOG and an organic type of siloxane based SOG. One of the commonly used organic type SOG materials is a silicon oxide based polysiloxane which is featured with radical groups replacing or attaching to oxygen atoms. Based on these two basic structures, the molecular weight, the viscosity and the desirable film properties of SOG can be modified and adjusted to suit the requirement of specific IC fabrication process.
SOG film is typically applied to a pre-deposited oxide surface as a liquid to fill gaps and steps on the substrate. Similar to the application method for photoresist films, a SOG material can be dispensed onto a wafer and spun at a rotational speed which determines the thickness of the SOG layer desired. After the film is evenly applied to the surface of the substrate, it is cured at a temperature of approximately 400xc2x0 C. and then etched back to obtain a smooth surface in preparation for a capping oxide layer on which a second interlevel metal may be patterned. The purpose of the etch-back step is to leave SOG between metal lines but not on top of the metal, while the capping oxide layer is used to seal and protect SOG during further fabrication processes. The siloxane based SOG material is capable of filling 0.15 micron gaps and therefore it can be used advantageously in 0.25 micron technology,
When fully cured, silicate SOG has similar properties like those of silicon dioxide. Silicate SOG does not absorb water in significant quantity and is thermally stable. However, one disadvantage of silicate SOG is the large volume shrinkage during curing. As a result, the silicate SOG retains high stress and cracks easily during curing and further handling. The cracking of the SOG layer can cause a serious contamination problem for the fabrication process. The problem can sometimes be avoided by the application of only a thin layer, i.e., 1000xcx9c2000 xc3x85 of the silicate SOG material.
In the current SOG coating process, a solvent edge rinse and a solvent backside rinse process are utilized to remove unwanted SOG deposited on the wafer edge and on the backside of the wafer. This is shown in FIGS. 1xcx9c3. A semiconductor wafer 10 which has a flat side 12 is shown in FIG. 1. After a SOG coating process, a SOG layer 14 is blanket deposited on the top surface 16 of the wafer. The layer is deposited as a dielectric layer for insulating between metal lines. In order to process the wafer in subsequent fabrication steps, the wafer must be positioned in reaction chambers for various processes such as etching or deposition. In most of the process chambers, the wafer is positioned on a platform and held down on the edge by a wafer clamp. The function of the wafer clamp is to prevent the wafer from moving during the process when reactant gases or etching gases may be flowing into the reaction chamber. To enable the wafer clamp to function properly, the edge portion of the wafer of approximately 2xcx9c4 mm wide must be cleaned without any coated material. The edge area 22 on wafer 10 is shown in FIG. 1.
In present wafer fabrication technology, the SOG layer deposited at unintended areas of the wafer can be removed in two different processes. The first process is a solvent edge rinse which is shown in FIG. 2. In this process, wafer 10 is placed on a platform (not shown) and spun at a predetermined rotational speed along a spin axis 26. The rotational speed of the wafer can be suitably adjusted for each specific application depending on the thickness of the layer to be removed and the type of chemical solution used. As shown in FIG. 2, a chemical solution injector 28 is used to inject chemical solution 32 onto the top edge 34 of the wafer. The chemical solution 38 deflected from the edge 34 of the wafer hits the chamber wall 42 and drains to the bottom of the process chamber. The solvent edge rinse process is effective in removing a limited area, i.e., a width of 2xcx9c4 mm, on the top edge of the wafer of an unwanted coating material such as SOG or photoresist.
The second cleaning process is a solvent backside rinse such as that shown in FIG. 3. The backside 48 of wafer 10 can be cleaned by this process. A cleaning solution 52 is injected from a spray nozzle 54 onto the backside 48 of the wafer. The process is also known as a centrifugal spray cleaning process wherein a chemical solution, i.e., normally a good solvent for the coating layer is pressure-fed and injected directly onto the backside of a spinning wafer. The process can be effectively used to reduce the volume of fresh chemical consumed and is normally faster than an immersion process. After the injected chemical solution 52 hits the bottom surface 48 of the wafer, the chemical solution 56 reflects from the backside 48 of the wafer and drains into the bottom of the process tank (not shown). During a normal backside rinse process, the sprayed chemical solution 52 is only capable of rinsing the backside 48 of the wafer and, none of the chemical solution 52 can reach the top surface 16.
After an edge bead rinse process is conducted on a processed silicon wafer 10, the concentricity of the rinse process must be determined in order to assure the quality of the IC dies (not shown) on the wafer 10. Traditionally, this is carried out by using a straight ruler 20 as shown in FIG. 4. The scales 24 on the straight ruler 20 is used to measure the edge rinse width 30. The measurement of the edge rinse width 30 may also be performed by using a caliper (not shown).
The measurement process for the edge rinse width 30 is an important step in the quality control of the edge bead rinse process. For instance, as shown in FIG. 5, when the concentricity of the SOG coating layer 14 is off in relationship to the wafer 10, serious quality problems occur in the numerous IC dies that are located on the edge of the wafer 10. Quality problems arising out of particle contamination may also result due to cracked SOG material. For instance, as shown in FIG. 5, portion 36 of the SOG coating layer resulting from a narrow edge rinse width 40 may cause SOG layer cracking issue in a subsequent process where wafer 10 is held down by a clamp ring (not shown). The excess SOG coating layer 36 when clamped under a ring crack and may cause serious particle contamination problem in a process chamber. On the other hand, at the opposite edge of the wafer 10, an excessively wide area 44 of the edge rinse width occurs in portion 46 of the SOG coating layer. The excessive removal of the SOG coating layer 14 results in some of the IC dies located in the area being damaged by a water jet that was used in the edge bead rinse process. The IC dies are damaged even when a small corner of the die is hit by the high velocity water jet.
A reliable measurement tool and a method for using such tool are therefore important issues in ascertaining the reliability of an edge bead rinse process. The concentricity of the edge bead rinse process in relationship to the wafer must be determined with high accuracy in order to calibrate the edge bead rinse apparatus, i.e., the position of the rinse nozzle. The calibration may be performed both at the beginning of an edge bead rinse process as a step in the set-up procedure, and during subsequent processes for checking reliability, i.e., the concentricity of the rinse pattern must be checked frequently to insure the reliability of the process. The conventional measurement technique of using a ruler or a caliper is inadequate in that it is not only time consuming and operator dependent but also inaccurate and requires many reading points along the circumferential edge of a wafer.
It is therefore an object of the present invention to provide a measurement tool for measuring the edge rinse width on a wafer without the shortcomings or drawbacks of the conventional measurement tools.
It is another object of the present invention to provide a measurement tool for edge rinse width on a wafer after an edge bead rinse process is conducted which can be readily used and is not operator dependent.
It is a further object of the present invention to provide a measurement tool for determining edge rinse width on a wafer after an edge bead rinse process is conducted which can be used in a single measurement step.
It is another further object of the present invention to provide a measurement tool for determining edge rinse width on a wafer after an edge bead rinse process is conducted which can be readily used to produce accurate readings.
It is still another object of the present invention to provide a measurement tool for determining edge rinse width on a wafer after an edge bead rinse process is conducted which can be fabricated of a substantially transparent sheeting material.
It is yet another object of the present invention to provide a measurement tool for determining edge rinse width on a wafer after an edge bead rinse process which incorporates multiple concentric marks placed juxtaposed to a circumferential edge of the wafer.
It is still another further object of the present invention to provide a method for measuring the width of a peripheral region on a disk which has a different optical appearance than the remaining areas on the disk by superimposing a substantially clear template having concentric circles marked on the template in different colors.
It is yet another further object of the present invention to provide a method for measuring the width of a peripheral region on a processed silicon wafer after an edge bead rinse process for determining the concentricity of the process in relationship to the wafer.
In accordance with the present invention, a template for measuring the edge width of a disk and a method for using such template are disclosed.
In a preferred embodiment, a template for measuring the edge width of a disk which is not covered by a coating layer on a top surface of the disk is provided which includes a substantially transparent sheet that has a contour substantially the same as the contour of the disk, a first mark made along a peripheral edge of the sheet at a first distance from the peripheral edge, and a second mark made along a peripheral edge of the sheet at a second distance from the peripheral edge, the second distance is larger than the first distance.
The template for measuring the edge width of a disk may further include a third mark made along a peripheral edge of the sheet at a third distance from the edge, the third distance is greater than the second distance. The disk may be a semiconductor wafer. The first mark and the second mark may be a continuous line having a line width smaller than 0.5 mm. The first mark and the second mark may further be color coded for ease of identification.
In the template for measuring the edge width of a disk, the first distance of the first mark may be less than 5 mm, while the second distance for the second mark may be less than 10 mm. The contour for the substantially transparent sheet may be circular. The coating layer on the top surface of the disk may be a photoresist layer or a spin-on-glass coating layer. The first mark may be a red line formed 2 mm from the peripheral edge, the second mark may be a green line formed 3 mm from the peripheral edge and the third mark may be a yellow line formed 4 mm from the peripheral edge. The edge width measured is an edge rinse width on a silicon wafer. The substantially transparent sheet may be formed of a clear plastic material.
The present invention is further directed to a method for measuring the width of a peripheral region on a disk that has a different optical appearance than the remaining areas on the disk which can be carried out by the operating steps of first providing a substantially transparent sheet which has a contour substantially the same as the contour of the disk, a first mark made along a peripheral edge of the sheet at a first distance from the peripheral edge, and a second mark made along a peripheral edge of the sheet at a second distance from the peripheral edge wherein the second distance is greater than the first distance, then positioning the substantially transparent sheet on top and substantially overlaps the disk, and comparing the positions of the first mark and the second mark with the width of the peripheral region on the disk which has the different optical appearance than the remaining areas on the disk such that a dimension of the peripheral region can be readily determined.
In the method for measuring the width of a peripheral region on a disk, the substantially transparent sheet may further include a third mark made along a peripheral edge of the sheet at a third distance larger than the second distance from the edge. The disk may be a silicon wafer coated with a photoresist layer that has the peripheral edge portion of the layer removed by an edge bead rinse process. The disk may further be a silicon wafer coated with a spin-on-glass coating layer which has the peripheral edge portion of the layer removed in an edge bead rinse process.
The method may further include the step of forming the first and the second mark in a continuous line which has a width smaller than 0.5 mm. The method may further include the step of forming the first and second mark in different colors for ease of identification. The method may further include the step of forming the first mark on the sheet at a first distance of less than 5 mm from the edge of the sheet. The method may further include the step of forming the second mark on the sheet at a distance of less than 10 mm from the edge of the sheet.
In the method, the contour of the substantially transparent sheet may be circular. The method may be used to measure an edge bead rinse width on a silicon wafer after a photoresist or SOG coating process. The method may further include the step of forming the first mark in a red line 2 mm from the circumferential edge, the second mark in a green line 3 mm from the circumferential edge and the third mark in a yellow line 4 mm from the circumferential edge of a silicon wafer. The method may further include the step of forming the substantially transparent sheet in a clear plastic material.